Shaped body made of fiber-reinforced composites having a segmented covering layer, its production and its use

Abstract

The present invention relates to shaped bodies made of fiber-reinforced ceramic composites and comprising a core zone and at least one covering layer which has a coefficient of thermal expansion which is higher than that of the core zone. The covering layer is an SiC-rich covering layer and is divided into segments which are separated from the adjacent segments by gaps or bridging zones of a material which is different from the material of the segments. The invention also relates to a process for producing such shaped bodies by infiltration of an intermediate body with molten silicon and their use for friction disks, in vehicle construction or as protective plates.

Description

FIELD OF THE INVENTION[0001]The invention relates to a shaped body made of fiber-reinforced ceramic composites which is built up of a core layer and at least one covering layer and whose matrix comprises predominantly silicon carbide (SiC), silicon (Si) and carbon (C) The invention also relates to a process for producing a shaped body made of fiber-reinforced composites and shaped bodies of this type which are configured as friction disks, brake disks or clutch disks. A particularly preferred embodiment of the invention comprises brake disks which are made up of C / SiC or C / C-SiC and in which the covering layer has a higher coefficient of thermal expansion or a higher SiC content than the core zone.BACKGROUND OF THE INVENTION[0002]C / SiC materials (ceramic materials which are reinforced with carbon fibers and have a matrix comprising SiC) for the shaped body of the invention include, inter alia, the materials described in the following documents: DE-A 198 56 721, DE-A 197 11 829 and D...

AI Technical Summary

Benefits of technology

[0019]According to the invention, the thermal stresses occurring within the individual segments are reduced compared to a coherent covering layer to such an extent that they can no longer lead to rupture within the region of the individual segments. Since the bridging zones comprise, according to the invention, materials which are different from those of the segments and have different thermophysical properties, the thermal stresses which occur can be transferred in a targeted manner into the region of the bridging zones, with both crack-containing and crack-free bridging zones being able to be realized.

Problems solved by technology

During the cooling from the silicon melt temperature (about 1420° C.) to room temperature (about 20° C.) necessary in the liquid silicization production process, the different coefficients of thermal expansion lead to thermally induced stresses which result in a pronounced pattern of cracks in the layer which are visible to the eye.

A disadvantage of the pattern of cracks known from the prior art in SiC-rich covering layers is that the cracks arising from the production process itself cannot be unambiguously distinguished from cracks which are newly formed as a result of cyclic thermal stress.

The visible cracks can therefore not be employed reliably as an early indicator of wear of the material.

In the case of C / SiC construction materials, a disordered pattern of cracks is undesirable for reasons of aesthetics, in the case of protective plates particularly because of the required function, since it gives an impression of lower product quality.

Images